The present invention relates generally to semiconductor device manufacturing and, more particularly, to a semiconductor device having a localized, extremely thin silicon-on-insulator channel region.
Semiconductor-on-insulator (SOI) devices, such as silicon-on-insulator devices (also abbreviated SOI in the art), offer several advantages over more conventional semiconductor devices. For example, SOI devices may have lower power consumption requirements than other types of devices that perform similar tasks. SOI devices may also have lower parasitic capacitances than non-SOI devices. This translates into faster switching times for the resulting circuits. In addition, the phenomenon of latchup, which is often exhibited by complementary metal-oxide semiconductor (CMOS) devices, may be avoided when circuit devices are manufactured using SOI fabrication processes. SOI devices are also less susceptible to the adverse effects of ionizing radiation and, therefore, tend to be more reliable in applications where ionizing radiation may cause operation errors.
The gain of a MOS transistor, usually defined by the transconductance (gm), is proportional to the mobility (μ) of the majority carrier in the transistor channel. The current carrying capability, and hence the performance of an MOS transistor is proportional to the mobility of the current-carrying carrier in the channel. The mobility of holes, which are the current-carrying carriers in a P-channel field effect (PFET) transistor, and the mobility of electrons, which are the current-carrying carriers in an N-channel field effect (NFET) transistor, may be enhanced by applying an appropriate stress to the channel. Existing stress engineering methods greatly enhance circuit performance by increasing device drive current without increasing device size and device capacitance. For example, a tensile stress liner and/or an embedded SiC source/drain region applied to an NFET transistor induces a longitudinal tensile stress in the channel and enhances the electron mobility, while a compressive stress liner and/or an embedded SiGe source/drain region applied to a PFET transistor induces a longitudinal compressive stress in the channel and enhances the hole mobility.
There are several process integration methods for the creation of dual stress films. The underlying theme is the blanket deposition of a first stress layer type, followed by lithography to mask and protect this first stress layer type, an etch to remove the first stress layer type where it is not desired, and then deposition of the second stress layer type. The resulting enhanced carrier mobility, in turn, leads to higher drive currents and therefore higher circuit level performance.
Ultrathin body silicon MOSFETs, such as ETSOI (extremely thin SOI) or FinFETs, are considered viable options for CMOS scaling for the 22 nanometer (nm) node and beyond. However, a thin-body SOI transistor such as an ETSOI transistor needs epitaxially grown, raised source/drain regions to achieve a sufficiently low transistor series resistance. Moreover, due to the extreme thinness of the ETSOI layer (e.g., on the order of about 6 nm or less), conventionally formed embedded source/drain stressors are not a viable means of inducing channel stress, as the trenches used to form embedded stressors are about 60-80 nm deep into the SOI layer. Consequently, it is a significant challenge to incorporate conventional stress layer techniques into such ultrathin film devices.